Volvo Penta (Zinc):Aluminium outboardes should be protected with zinc anodes in sea water; as aluminium anodes produce alkalinity at the cathode which can effect the aluminium casing. Magnesium Anodes are avalible for fresh water environments.Z-guard offers a full range of equivalent zinc and magnesium anodes for Volvo Penta, OMC-Johnson-Evinrude, Mercruiser-Mercury, Mariner-Yamaha, Suzuki, Yanmar, Honda, Bukh, Vetus, Arneson, Hamilton etc.